Paint-ball guns fire a plastic-walled, paint- or gelatin-filled projectile using compressed gas as the source of power to accelerate the paint ball down a chamber and into a gun barrel. The paint ball enters the barrel from a hopper at the breech end, is accelerated by compressed gas, and exits the muzzle of the barrel.
Prior art in the area of air-powered guns, and especially paint-ball guns, uses canisters of liquid CO2 or other compressed gas communicated through regulators to provide a regulated gas pressure to the gun.
Since paint balls may thus have different diameters due to manufacturing tolerances and expansion because of heat or humidity, paint-ball guns typically use a “ball sizer” attachment between the breech of the gun and the barrel. The paint ball enters the ball sizer first and is accelerated there by gas pressure to essentially its maximum velocity before entering the barrel of the gun. The user chooses a ball sizer of the appropriate diameter to match as nearly as possible the size of the paint balls he is using at that time. Ball sizers typically connect with a barrel and with the breech of the gun with threaded joints.
It is important that the transition of the ball from the ball sizer to the barrel take place smoothly, so the ball is not torn or set spinning arbitrarily when it enters the breach of the barrel.